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During discharging the electrochemical energy stored in the electrodes is converted to
electrical energy.  The electrochemical reactions during discharging, results in water and
Lead Sulfate which coats both electrodes, recharging restores the situation.

While charging electrolysis of water decomposes, as a byproduct, water to its ingredients.
Oxygen gas is formed at the positive plate and Hydrogen gas at the negative plate.


Flooded Lead Acid Battery.

In Flooded, also called Wet , or Conventional  Batteries, the oxygen and hydrogen gases
formed during charging are vented to the air. They  therefore require periodic maintenance,
performed by authorized personnel, in order to check the sate of the battery and refill the
missing water, if needed.
Due to hydrogen’s explosive nature the batteries should be located in separate unmanned
and well vented rooms. These  are generally used only in large installations, where long life
and cost /performance predominate, and where maintenance personnel is available.  


Maintenance Free Valve Regulated (VRLA), Sealed Lead Acid ( LSA)
Batteries

In a Sealed  Battery, the possibility of gas venting to the air is eliminated. The oxygen
diffuses through the separator from the positive plate to the negative plate, where it is
recombined with the hydrogen to form water. These batteries do not require water
refilling and are therefore called also Maintenance Free batteries.

To enable the possibility of pressure relief, mainly during overcharging,   relief valves are
installed, to regulate to preset pressure level. Thus, UPS SLA batteries  are frequently  
called Valve Regulated Lead Acid (VRLA) type.

SLA batteries are considered dry type, generally spill proof and leak proof even in case of
container cracks or fractures. They can be located within the UPS as any other electrical
component.

Following features of the SLA  type cause manufactures’ to prefer VRLA technology for
Uninterruptible Power Supply  applications:  

  • Maintenance free, no water topping up is required during the whole service life.
          No equalization charge is normally required.

  • Non hazardous, have no restrictions for rail, road, sea or air transportation as part
          of the system or as separate items.

  • Rugged and vibration resistant. Can be shipped via parcel post or fast shipping
    service.

  • Non corrosive can be used for marine applications or wet environment.

  • Can be located in any position (horizontal or vertical), enabling design flexibility.

  • Allow location adjacent to each other or on top of each other (provided that weight
    and venting are considered). Compact packaging in the enables using internal
    batteries while increasing capacity and backup time.

  •  About 99% of the gas is recombined within the battery; practically no hydrogen is
    emitted to the air, can be located in manned locations, where normal venting exists.

  •  The UPS can be designed to allow replacement or hot swapping of failed batteries
    by the operators, or by local service people.

  •  High rate discharge ability. As requested for systems that provide high energies for
    relatively short times.

  • No memory effect. VRLA batteries retain their full charge in float condition during  
    lifetime.
Operation and  Features of  Maintenance Free and Flooded  
UPS Power Supply Battery
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